(1) Field of the Invention
This invention relates to an optical disc used for recording video data, a recording apparatus, and a computer-readable recording medium recording a file management program.
(2) Description of the Prior Art
Recently, optical discs such as CD-ROMs and DVD (Digital Versatile Disc)-ROMs have been used for recording video data (also called AV data in this document) of movies or the like, as well as being used as secondary storages for computers. Currently, practical uses of DVD-RAMs are awaited because of the general expectation that DVD-RAMs will be popular as the main recording medium of the next generation.
First, conventional DVD-ROMs are explained in terms of special reproductions. The special reproductions include fast forwarding or rewinding AV data at a speed n times as high as the normal reproduction speed (hereinafter such a speed is called n-speed).
The AV data to be recorded in DVD-ROMs is compressed with a compression encoding method at a variable bit rate to increase the compression rate. The xe2x80x9cvariable bit ratexe2x80x9d means that the amount of compressed image data per one frame is variable. As a result, the amount of compressed data is not proportionate to the reproduction period. When this happens, even if the coded AV data is read out at steady intervals, that is at every predetermined size of the coded AV data, the read-out AV data does not correspond to images to be sectioned per predetermined time period.
To relate the amount of compressed data to the reproduction period, information of each special reproduction is inserted into necessary points in the AV data in DVD-ROMs.
More specifically, the AV data is compressed in compliance with MPEG2. Through the compression, information called NV pack which is unique to DVD is added to the start of each GOP (Group of pictures). GOPs are sections which each have a period of 0.4 to 1.0 seconds. Exceptionally, an end of a VOB (video object) has a GOP of 1.2 seconds. Data included between one NV pack and the next NV pack is called VOBU (Video Object Unit).
Each NV pack includes 2K-bytes of information used for referring to adjacent NV packs. Each NV pack also includes the data size of the first reference picture in a GOP. The information used for referring to adjacent NV packs is composed of relative addresses of NV packs of VOBUs in the forward and backward directions separated by a predetermined time period from the current VOBU, the relative addresses being obtained based on the start time code of the current VOBU. The predetermined time period may be one to 15, 20, 60, 120, and 240 seconds.
Secondly, operations of special reproductions such as fast forwarding and rewinding are described. The special reproductions substantially at a steady speed are attained by reproducing only the reference pictures of VOBUs having a predetermined time interval in between, in accordance with the reproduction speed. To sequentially read out the VOBUs having a predetermined time interval in between, the information used for referring to adjacent NV packs in each NV pack is used.
A time search map is recorded in every time code that is arranged with a predetermined time interval in between from the start of the AV data. The time search map indicates an address of a piece of AV data in the VOBU corresponding to the current time code. By referring to the time search maps, reproduction apparatuses can start reproducing the AV data starting from the specified time codes.
However, it has been impossible to apply the method of inserting the special reproduction information into AV data to real-time recording of data into recording mediums such as DVD-RAMs.
This is because in real-time recording of AV data, information on a part of the AV data to be recorded from now on (e.g., addresses of NV packs in the backward direction) cannot be obtained.
Also, it is possible to generate special reproduction information to be recorded in each NV pack after the AV data is recorded. However, to record the generated information into an AV data storage area as NV packs, the same number of accesses to the disc as the number of VOBUs are required. This cannot be achieved in real time.
Some may think that this problem will be solved by storing the AV data and the special reproduction information in different AV data areas. However, this solution has another problem that to store the special reproduction information in a main memory, the main memory should have a large capacity, where the storage of the special reproduction information in the main memory is necessary to execute the special reproductions at high speed.
It is therefore an object of the present invention to provide an optical disc recording apparatus for generating special reproduction information of reduced amount while AV data is recorded onto the disc in real time, and an optical disc onto which data is recorded by the optical disc recording apparatus.
The above object is achieved by an optical disc including a data area and a time map area, the data area storing one or more video objects and the time map area storing time map information, where each video object includes a plurality of video object units. The time map information includes a first time table and a second time i.e., a pair of time tables for each video object. Each first time table includes: addresses of video object units in a corresponding video object, the addresses being arranged in order and indicating storage positions of the video object units that correspond to reproduction points that differ by a predetermined time unit, the predetermined time unit being longer than a maximum reproduction period of a video object unit; and indicators for specifying the video object units which respectively correspond to the addresses. Each second time table includes an entry for each video object unit in the corresponding video object, the entries being arranged in order and each including a reproduction period of a video object unit and a data size of the video object unit.
With the above construction, the first time table has a small size since the first time table only records storage positions of video object units at predetermined intervals. For the second time table, it is not required to record a storage position of each video object unit in relation with a reproduction point. The second time table also includes a reproduction period and a data size for each video object unit. As a result, the second time table also has a small size since the reproduction period is smaller than the data size. It is very easy to generate the second time table while data is recorded onto the disc since the second time table is recorded in units of video object units which are the unit of encoding.
In the above optical disc, each first time table may include a plurality of first time maps which each correspond to a different one of the reproduction points, and each second time table may include a plurality of second time maps which each correspond to a different one of the plurality of video object units. Each first time map includes: one of the indicators, the indicator indicating a second time map for a video object unit that corresponds to the reproduction point, an address of the video object unit that corresponds to the reproduction point, and difference information indicating a difference between the corresponding reproduction point and a reproduction start time of the corresponding video object unit. Each second time map includes time information indicating a reproduction period of a corresponding video object unit, and also includes a data size of the corresponding video object unit.
In the above optical disc, the time map information may include a time offset for each video object, each time offset indicating a difference between a first reproduction point during a reproduction of the corresponding video object and a start time of a first video object unit in the corresponding video object.
With the above construction, it is possible to correct the time map information without difficulty by changing the value of the time offset even if the first part of a video object is cut by editing.
The above object is also achieved by a recording apparatus including: an input unit for receiving video data in a time series; a compression unit for compressing the received video data to generate a video object which includes a sequence of video object units; a write unit for writing data onto an optical disc; and a control unit for controlling the write unit, where the control unit controls the write unit to write the generated video object onto the optical disc, generates a first time table and a second time table, and controls the write unit to write the generated first time table and second time table. Each first time table includes: addresses of video object units in a corresponding video object, the addresses being arranged in order and indicating storage positions of the video object units that correspond to reproduction points that differ by a predetermined time unit, the predetermined time unit being longer than a maximum reproduction period of a video object unit; and indicators for specifying the video object units which respectively correspond to the addresses. Each second time table includes an entry for each video object unit in the corresponding video object, the entries being arranged in order and each including a reproduction period of a video object unit and a data size of the video object unit.
With the above construction, the first time table has a small size since the first time table only records storage positions of video object units at predetermined intervals. For the second time table, it is not required to record a storage position of each video object unit in relation with a reproduction point. The second time table also includes a reproduction period and a data size for each video object unit. As a result, the second time table also has a small size since the reproduction period is smaller than the data size. It is very easy to generate the second time table while data is recorded onto the disc since the second time table is recorded in units of video object units which are the unit of encoding.
In the above recording apparatus, each first time table may include a plurality of first time maps which each correspond to a different one of the reproduction points, and each second time table may include a plurality of second time maps which each correspond to a different one of the plurality of video object units. Each first time map includes: one of the indicators, the indicator indicating a second time map for a video object unit that corresponds to the reproduction point, an address of the video object unit that corresponds to the reproduction point, and difference information indicating a difference between the corresponding reproduction point and a reproduction start time of the corresponding video object unit. Each second time map includes time information indicating a reproduction period of a corresponding video object unit, and also includes a data size of the corresponding video object unit.
In the above recording apparatus, the time map information may include a time offset for each video object, each time offset indicating a difference between a first reproduction point during a reproduction of the corresponding video object and a start time of a first video object unit in the corresponding video object.
With the above construction, it is possible to correct the time map information without difficulty by changing the value of the time offset even if the first part of a video object is cut by editing.